Airflow sensor for a heat sink

ABSTRACT

An airflow sensor for a heat sink has a substantially flat base portion and a deformable upper portion electrically coupled to the base portion that contacts a conductive strip. As airflow increases, the deformable upper portion deforms and moves away from the source of airflow, which moves the point of contact between the deformable upper portion and the conductive strip farther away from the source of the airflow. The difference in the point of contact is measured, and is used to characterize the airflow sensor for different airflows. Data from the airflow sensor can then be logged during system operation. When needed, the data from the airflow sensor can be read from the log and converted to airflow using the airflow sensor characterization data. In this manner the airflow through a heat sink may be dynamically measured, allowing analysis and correlation between system events and airflow through the heat sink.

BACKGROUND

1. Technical Field

This disclosure generally relates to airflow sensors, and morespecifically relates to an airflow sensor for a heat sink.

2. Background Art

Heat sinks are commonly used in modern electronic systems to dissipateheat generated by electronic components, such as processors. A source ofair such as a fan is typically placed in proximity to a heat sink toproduce airflow over the heat sink, which enhances the ability of theheat sink to dissipate heat.

Modern heat sinks are typically modeled using thermal simulation.Prototypes are then built, which are qualified with thermal testvehicles and flow benches. However, even with thermal simulation andflow bench qualification, a heat sink may behave differently in a systemthan modeled. Oftentimes the internal environment is difficult topredict and model.

SUMMARY

An airflow sensor for a heat sink has a substantially flat base portionand a deformable upper portion electrically coupled to the base portionthat contacts a conductive strip. As airflow increases, the deformableupper portion deforms and moves away from the source of airflow, whichmoves the point of contact between the deformable upper portion and theconductive strip farther away from the source of the airflow. Thedifference in the point of contact is measured, and is used tocharacterize the airflow sensor for different airflows. Data from theairflow sensor can then be logged during system operation. When needed,the data from the airflow sensor can be read from the log and convertedto airflow using the airflow sensor characterization data. In thismanner the airflow through a heat sink may be dynamically measured,allowing analysis and correlation between system events and airflowthrough the heat sink.

The foregoing and other features and advantages will be apparent fromthe following more particular description, as illustrated in theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING(S)

The disclosure will be described in conjunction with the appendeddrawings, where like designations denote like elements, and:

FIG. 1 is a side view of an airflow sensor for a heat sink;

FIG. 2 is a side view of the airflow sensor of FIG. 1 showing how thecontact point moves with airflow;

FIG. 3 is a side view of the airflow sensor of FIG. 1 mounted betweentwo fins on a heat sink;

FIG. 4 is a flow diagram of a method for characterizing an airflowsensor;

FIG. 5 is a flow diagram of a method for logging information as anelectronic system runs;

FIG. 6 is a flow diagram of a method for determining airflow in anelectronic system using the airflow sensor; and

FIG. 7 is a block diagram of an electronic system that includes a heatsink with an airflow sensor as described and claimed herein.

DETAILED DESCRIPTION

The disclosure and claims herein relate to an airflow sensor for a heatsink that has a substantially flat base portion and a deformable upperportion electrically coupled to the base portion that contacts aconductive strip. As airflow increases, the deformable upper portiondeforms and moves away from the source of airflow, which moves the pointof contact between the deformable upper portion and the conductive stripfarther away from the source of the airflow. The difference in the pointof contact is measured, and is used to characterize the airflow sensorfor different airflows. Data from the airflow sensor can then be loggedduring system operation. When needed, the data from the airflow sensorcan be read from the log and converted to airflow using the airflowsensor characterization data. In this manner the airflow through a heatsink may be dynamically measured, allowing analysis and correlationbetween system events and airflow through the heat sink.

Referring to FIG. 1, an airflow sensor 100 comprises a base portion 110electrically coupled to a deformable portion 120 that contacts anelectrically conductive strip 130. In the most preferred implementation,the base portion 110 and the deformable portion 120 are made from asingle piece of material, such as metal. The deformable portion 120 isdesigned so when there is no airflow present, the deformable portion 120contacts the conductive strip 130 at a first point 140 shown in FIG. 1.The base portion 110 includes a first point of electrical contact 150and the conductive strip 130 includes a second point of electricalcontact 160. Measuring resistance between the first and secondelectrical points of contact 150 and 160 results in a first resistancereading. The contact point 140 for the deformable portion when there isno airflow present is shown at a distance d1 in FIG. 1 from the point ofcontact 160 on the conductive strip 130.

The deformable portion 120 is deformable under the force of airflow.Referring to FIG. 2, in the presence of airflow represented as 210 inFIG. 2, deformable portion 120 deforms into a shape that moves the pointof contact between the deformable portion 120 and the conductive strip130 to a point 220 that is farther away from the airflow than the point140 in FIG. 1 when there is no airflow present. Point 220 in FIG. 2 isshown at a distance d2 from the point of contact 160 on the conductivestrip 130, which is farther away from the airflow 210 than distance d1for contact point 140 shown in FIG. 1. The result of the deformableportion moving its contact point from 140 in FIGS. 1 to 220 in FIG. 2due to the force of airflow 210 is a second resistance reading betweenthe first and second electrical contact points 150 and 160 that isgreater than the first resistance reading in FIG. 1. This difference inelectrical resistance can be measured and used to determine airflowacross the airflow sensor 100.

FIGS. 1 and 2 show side views of the airflow sensor 100, which does notindicate the width of the airflow sensor 100 that would be in contactwith the airflow 210. At one extreme, the airflow sensor 100 could havea cross-section with respect to the airflow 210 that is very small,meaning the airflow sensor 100 could have a width of a human hair orless. At the other extreme, the airflow sensor 100 could have across-section with respect to the airflow 210 that is significant,meaning the airflow sensor 100 substantially disrupts the airflow 210.In the most preferred implementation, the airflow sensor 100 has ageometry resembling a flat ribbon that is preferably more than amillimeter and less than ten millimeters wide. This flat ribbon geometryallows sufficient surface area for the airflow 210 to deform thedeformable portion 120 without significantly disrupting the airflow 210.In addition, thickness of the ribbon could be adjusted according toairflow ranges. Thus, a thicker ribbon could be used to provide areasonable deformation across the range of airflow when the expectedairflow is high. A thinner ribbon could be used when the expectedairflow is low. Using an appropriate specific design of airflow sensor100 allows measuring airflow without significantly disrupting theairflow.

The airflow sensor 100 could be made from any suitable material orcombination of materials. In the most preferred implementation, the baseportion 110, the deformable portion 120, and the conductive strip 130are all made of the same material. In the most preferred implementation,the preferred material is metal, such as copper, nickel, indium or tin.Of course, alloys of different metals could also be used. In addition,non-metallic conductors or semiconductors could also be used.Furthermore, the base portion 110, deformable portion 120 and conductivestrip 130 could be made of different materials. Any suitable materialsfor the airflow sensor 100 could be used as long as the deformableportion 120 deforms under the force of airflow and a difference inresistance is generated due to differences in airflow.

The airflow sensor 100 shown in FIGS. 1 and 2 can be used to measureairflow on a heat sink. Referring to FIG. 3, two fins 310 and 320 of aheatsink 300 are shown. Of course, the heat sink 300 could include otherfins not shown in FIG. 3. The airflow sensor 100 is placed between fins310 and 320 by bonding the conductive strip 130 to a lower surface offin 310 and by bonding the base portion 110 to the upper surface of fin320, as shown in FIG. 3. In one suitable implementation, either the baseportion 110 could be electrically coupled to the fin 320 or theconductive strip 130 could be electrically coupled to the fin 310. Inthe most preferred implementation, both base portion 110 and conductivestrip 130 are electrically insulated from the fins 310 and 320.

In the configuration shown in FIG. 3, the airflow sensor 100 willproduce different values of electrical resistance with different amountsof airflow between the first fin 310 and second fin 320. Because theairflow sensor 100 minimally disrupts the airflow, the airflow sensor100 provides crucial airflow information for a heat sink in an operatingenvironment in a manner that does not significantly negatively impactthe performance of the heat sink.

The placement of the airflow sensor 100 in FIG. 3 is shown on the leftedge of the heatsink. Note, however, the airflow sensor 100 could beplaced anywhere along the length of the heatsink 300 provided there isno obstruction to the airflow. Thus, airflow sensor 100 in FIG. 3 couldbe moved to the middle of heat sink 300 or to the right edge of heatsink300. The disclosure and claims herein extend to any suitable locationfor the airflow sensor 100 on a heat sink 300.

While it is possible the airflow sensor 100 could be designed to provideresistance between the two electrical points 150 and 160 that islinearly proportional to airflow, other designs that do not provide suchlinear proportionality could also be used. In the most preferredimplementation, the airflow sensor is tested and characterized so itsperformance is known, and future readings can be compared to thecharacterization data to determine airflow. Referring to FIG. 4, method400 begins by attaching an airflow sensor to a heat sink (step 410),such as the configuration shown in FIG. 3. Next, the heat sink is placedon a flow bench, and a particular airflow is selected (step 420). Theselected airflow is then run over the heat sink (step 430). The airflowsensor reading is recorded for the known airflow (step 440). We assumesteps 420, 430 and 440 are repeated for several different airflows, sostep 450=NO, and these steps are repeated with a different selectedairflow. This characterization of airflow sensor readings to airflowcontinues until characterization of the airflow sensor is complete (step450=YES), at which point the airflow sensor readings are stored asairflow sensor characterization data (step 460). The airflow sensorcharacterization data stored in step 460 can then be used to determineairflow over the airflow sensor at any given point in time based on theelectrical resistance readings of the airflow sensor.

Electronic systems often log performance data. Referring to FIG. 5,method 500 monitors and logs performance data for an electronic system(step 510), and additionally logs the airflow sensor readings (step520). Logging airflow sensor readings at the same time other performanceparameters are logged provides data from which airflow can be determinedat particular points in time that correlate to the logged performancedata.

Referring to FIG. 6, a method 600 begins by reading the loggedperformance data (step 610). When airflow for the logged performancedata is not needed (step 620=NO), method 600 is done. For example, ifthe logged performance data is read in step 610 to determine memoryutilization at a particular point in time, airflow will not affectmemory utilization, so the airflow information is not needed. Whenairflow for the logged performance data is needed (step 620=YES), thelogged airflow sensor readings are read (step 630), then converted toairflow using the airflow sensor characterization data (step 640).Method 600 thus provides logged performance data correlated withairflow, which allows determining whether airflow could have contributedto a logged event. For example, when a processor experiences a powerthrottling event, knowing the airflow at the time of the power throttlecould provide an indication of whether proper airflow was being appliedto the heat sink.

Referring to FIG. 7, an electronic system 710 is shown, which includeselectronic components 720. Electronic components 720 can include anytype of electronic components, systems or subsystems, including withoutlimitation processors, memory, integrated circuits, discrete logic, harddisk drives, I/O adapters, etc. A performance measurement mechanism 780monitors and logs data in a performance measurement log 790. A heat sink730 is provided for one or more of the electronic components 720 thatincludes an airflow sensor 740. Airflow sensor 100 shown in FIGS. 1-3 isone suitable implementation for airflow sensor 740 in FIG. 7. Theairflow sensor 740 is connected to an airflow sensor measurementmechanism 750, which measures readings from the airflow sensor 740. Inone suitable implementation, the readings could be electricalresistance. In another suitable implementation, the airflow sensormeasurement mechanism 750 could measure a voltage across the airflowsensor 740. When steps are taken to characterize an airflow sensor asshown in method 400 in FIG. 4, the airflow sensor characterization datastored in step 460 is represented as 760 in FIG. 7. An airflow sensormeasurement log 770 preferably includes airflow sensor measurements overtime. In the most preferred implementation, both the performancemeasurement log 790 and airflow sensor measurement log 770 havetimestamped entries that allow correlating the two. Thus, if theperformance measurement mechanism 780 determines processor temperaturerose at a given point in time, the airflow sensor measurement log 770can be consulted to determine the airflow through the processor'sheatsink at the same point in time. Correlating airflow to logged systemevents thus provides a way to determine whether airflow was acontributing factor in the logged system events.

Many variations are possible within the scope of the disclosure andclaims herein. For example, while a single airflow sensor on a singleheatsink is shown in FIG. 3, multiple airflow sensors could be used on asingle heatsink, and a single airflow sensor could be used between twoadjacent heatsinks. The use of multiple airflow sensors in differentregions of a heatsink could be very helpful in testing andcharacterizing performance of a heat sink. In addition, multiple airflowsensors that have different properties could be used together. Forexample, three airflow sensors could be used on a heat sink, with afirst airflow sensor that measures airflow up to a first threshold, asecond airflow sensor that measures airflow from the first threshold toa second threshold, and the third airflow sensor that measure airflowfrom the second threshold to a third threshold. The disclosure andclaims herein expressly extend to any suitable number of airflow sensorsin any suitable configuration for measuring airflow on one or more heatsinks.

An airflow sensor for a heat sink has a substantially flat base portionand a deformable upper portion electrically coupled to the base portionthat contacts a conductive strip. As airflow increases, the deformableupper portion deforms and moves away from the source of airflow, whichmoves the point of contact between the deformable upper portion and theconductive strip farther away from the source of the airflow. Thedifference in the point of contact is measured, and is used tocharacterize the airflow sensor for different airflows. Data from theairflow sensor can then be logged during system operation. When needed,the data from the airflow sensor can be read from the log and convertedto airflow using the airflow sensor characterization data. In thismanner the airflow through a heat sink may be dynamically measured,allowing analysis and correlation between system events and airflowthrough the heat sink.

One skilled in the art will appreciate that many variations are possiblewithin the scope of the claims. Thus, while the disclosure isparticularly shown and described above, it will be understood by thoseskilled in the art that these and other changes in form and details maybe made therein without departing from the spirit and scope of theclaims.

The invention claimed is:
 1. An airflow sensor comprising: a baseportion having a first electrical point of contact; and a deformableupper portion electrically coupled to the base portion, wherein thedeformable upper portion contacts an electrically conductive stripopposite the base portion at a first contact point when there is noairflow, wherein airflow deforms the deformable upper portion so thedeformable upper portion contacts the conductive strip at a secondcontact point farther away from a source of the airflow, wherein theconductive strip comprises a second electrical point of contact, andmeasurement is made between the first and second electrical points ofcontact to determine airflow through the airflow sensor.
 2. The airflowsensor of claim 1 wherein electrical resistance between the first andsecond electrical points of contact is a function of airflow through theairflow sensor.
 3. The airflow sensor of claim 1 wherein voltage betweenthe first and second electrical points of contact is a function ofairflow through the airflow sensor.
 4. The airflow sensor of claim 1wherein the base portion, deformable upper portion and conductiveportion are made of the same electrically conductive material.
 5. Theairflow sensor of claim 4 wherein the electrically conductive materialcomprises metal.
 6. The airflow sensor of claim 1 wherein the baseportion and deformable upper portion are made from a single piece ofmaterial.
 7. A heat sink comprising: a first thermally-conductive fin; asecond thermally-conductive fin substantially parallel to and underlyingthe first thermally-conductive fin and thermally coupled to the firstthermally-conductive fin; an airflow sensor comprising: an electricallyconductive strip coupled to a bottom surface of the firstthermally-conductive fin, wherein the conductive strip comprises a firstelectrical point of contact; a base portion coupled to a top surface ofthe second thermally-conductive fin, the base portion comprising asecond electrical point of contact; and a deformable upper portionelectrically coupled to the base portion, wherein the deformable upperportion contacts the electrically conductive strip at a first contactpoint when there is no airflow, wherein airflow deforms the deformableupper portion so the deformable upper portion contacts the conductivestrip at a second contact point farther away from a source of theairflow, and measurement is made between the first and second electricalpoints of contact to determine airflow through the airflow sensor.